The present invention relates to suspension systems employed with powered wheelchairs, and more particularly, to suspension systems which adapt to various operating conditions of the wheelchair.
Powered wheelchairs having drive systems incorporating anti-tip wheels coupled to the wheelchair frame for movement up and down relative to a surface supporting the wheelchair are known in the art. For example, U.S. Pat. No. 6,129,165 to Schaffner et al., assigned to Pride Mobility Products Corporation of Exeter, Pennsylvania, discloses a wheelchair having a drive system including a drive assembly which is coupled to anti-tip wheels pivotally mounted to the wheelchair frame. The anti-tip wheels pivot up and down relative to the supporting surface in response to moments created by the drive motors during acceleration or deceleration of the wheelchair. It would be desirable that a wheelchair having pivotally mounted anti-tip wheels provide variable resistance to movement of the wheels depending upon the operating condition of the wheelchair. For example, if the wheelchair is operating on a downward incline, it would be desirable that resistance to movement of the anti-tip wheels be increased to retard upward movement of the anti-tip wheels and thus promote stability of the wheelchair. Similarly, when the wheelchair is climbing a curb or other obstacle, it would be desirable that the resistance to upward movement of the anti-tip wheels be minimized to facilitate movement of the anti-tip wheels over the obstacle. A need exists for a wheelchair wheel suspension system having variable stiffness characteristics.